[PAT] A1099 Build A Binary Search Tree

题目大意

给出二叉搜索树的树型和各个节点值，求出该树的后序遍历结果。

思路

用静态结构体数组表示树。序列按照值从小到大即树的中序遍历结果。根据输入确定树型，在中序遍历的过程中填入值。接着层序遍历一次输出即可。（也可遍历时标记满二叉树情况下的index，根据index值从大到小输出即为层序遍历结果）

AC代码

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include <cstdio>
#include <vector>
#include <map>
#include<algorithm>
#include<queue>
#include <cstring>
using namespace std;
struct Node {
	int key;
	int lchild, rchild;
}node[100];
vector<int>in;
int t = 0;
void in_insert(int v) {
	if (node[v].lchild != -1)in_insert(node[v].lchild);
	node[v].key = in[t];
	t++;
	if (node[v].rchild != -1)in_insert(node[v].rchild);
}
void levelorder() {
	queue<int>q;
	q.push(0);
	bool space = false;
	while (!q.empty()) {
		int v = q.front();
		q.pop();
		if (space == false) {
			printf("%d", node[v].key);
			space = true;
		}
		else {
			printf(" %d", node[v].key);
		}
		if (node[v].lchild != -1)q.push(node[v].lchild);
		if (node[v].rchild != -1)q.push(node[v].rchild);
	}
}
bool cmp(int a, int b) {
	return a < b;
}
int main() { 
	int n, i;    
	scanf("%d", &n);    
	for (i = 0;i < n;i++) {
		scanf("%d%d", &node[i].lchild, &node[i].rchild);
	}
	int value;
	for (i = 0;i < n;i++) {
		scanf("%d", &value);
		in.push_back(value);
	}
	sort(in.begin(), in.end(), cmp);
	in_insert(0);
	levelorder();
	return 0; 
}

不用层次遍历，直接赋值index的方法。代码如下：

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include <cstdio>
#include <vector>
#include <map>
#include<algorithm>
#include<queue>
#include <cstring>
using namespace std;
struct Node {
	int key;
	int lchild, rchild;
	int index, lebel;
}node[100];
vector<int>in;
int t = 0;
void in_insert(int v, int index, int lebel) {
	if (node[v].lchild != -1)in_insert(node[v].lchild, index * 2 + 1, lebel + 1);
	node[v].index = index;
	node[v].lebel = lebel;
	node[v].key = in[t];
	t++;
	if (node[v].rchild != -1)in_insert(node[v].rchild, index * 2 + 2, lebel + 1);
}
bool cmp(int a, int b) {
	return a < b;
}
bool cmpindex(Node a, Node b) {
	if (a.lebel != b.lebel)return a.lebel < b.lebel;
	return a.index < b.index;
}
int main() { 
	int n, i;    
	scanf("%d", &n);    
	for (i = 0;i < n;i++) {
		scanf("%d%d", &node[i].lchild, &node[i].rchild);
	}
	int value;
	for (i = 0;i < n;i++) {
		scanf("%d", &value);
		in.push_back(value);
	}
	sort(in.begin(), in.end(), cmp);
	in_insert(0, 0, 0);
	sort(node, node + n, cmpindex);
	printf("%d", node[0].key);
	for (i = 1;i < n;i++)
		printf(" %d", node[i].key);
	return 0; 
}

疑问：为啥如果不用lebel，就会有两个测试点（1、2）过不了？？？求路过的大神帮忙解答一下，万分感激！！！